1. Field of the Invention
This invention relates generally to monofilaments, and more particularly to monofilaments having split ends, which may be used for example as toothbrush bristles.
2. Description of the Related Art
Thermoplastic polymers have long been used to form brush bristles in a wide variety of configurations. To increase the effectiveness of these brushes, the ends of such bristles have been split or xe2x80x9cfeatheredxe2x80x9d to provide a soft bristle tip. In the past, however, various difficulties have been encountered in splitting bristle tips.
In particular, various techniques have been used to split paintbrush bristles to improve painting performance. Such procedures have been particularly suited to paintbrush bristles because long splits which propagate along a large portion (up to one inch) are particularly desirable. With certain brushes, however, only splitting of the tips is desirable. For example, the length of a typical toothbrush bristle is about (or less than) one half inch. If splitting were to occur along a large portion of a toothbrush bristle, the bristles would not be sufficiently rigid to adequately clean teeth. Accordingly, currently available splitting techniques fail to adequately address difficulties associated with splitting the tips of toothbrush bristles and other bristles in which long splits are undesirable.
This invention relates to a monofilament having a portion with a plurality of internal fusion lines and at least four voids, wherein the voids comprise between 5 and 20% of the cross-sectional area of the monofilament.
This invention also relates to a monofilament having a diameter in a range of 0.0025 to 0.012 inches, wherein the monofilament has a hexalocular, an octalocular, or a near circular shape.
In addition, this invention relates to a method of manufacturing extruded monofilaments having split ends, including the steps of extruding a plurality of thermoplastic polymeric streams to form a plurality of monofilaments, spinning a plurality of cutting blades above 1000 rpm, and placing a plurality of cutting blades in contact with end portions of the monofilaments to form split ends. In one embodiment of the present invention, the blades are spun at or near the natural frequency of the monofilaments.